Continuously variable transmission system

ABSTRACT

A continuously variable transmission (CVT) system, which turns the rear wheels of a lawn mower or similar vehicle at different speeds in a coordinated method with the front steering wheels in order to achieve the best turning radius (including a tight or zero turn radius, if desired) under most conditions. The system comprises two stages: the first stage comprising a Fixed Center Distance CVT pulley system, and the second stage comprising dual CVTs (e.g., left and right) that input into dual gear reducers (left and right), which are mechanically connected to the rear wheels. The second stage dual CVTs (left and right) are synchronized with the steering wheel, thus achieving different rear wheel speeds and/or directions based on the steering wheel position.

This application is a continuation of U.S. application Ser. No.15/076,758, filed Mar. 22, 2016, which is a continuation of U.S.application Ser. No. 13/903,640, filed May 28, 2013, by Dennis Brandon,which claims benefit of and priority to U.S. Provisional Application No.61/652,313, filed May 28, 2012, by Dennis Brandon, and is entitled tothose filing dates for priority. The specifications, figures andcomplete disclosures of U.S. Provisional Application No. 61/652,313 andU.S. application Ser. Nos. 15/076,758 and 13/903,640 are incorporatedherein by specific reference for all purposes.

FIELD OF INVENTION

This invention relates to a continuously variable transmission systemfor use with riding lawnmowers and other vehicles to achieve a smallturning radius or zero turn radius.

BACKGROUND OF THE INVENTION

A tight turning radius is very important for riding lawnmowers to mowgrass around objects such as trees. Zero turn mowers are very good formowing around objects since their turning radius is very small. However,the cost of a zero turn mower is very high compared to typical ridinglawnmowers, and the driving of a zero turn mower using two levers isperceived to be difficult for many consumers. Further, the hydrostatictransmissions are very inefficient. Most zero turn mowers have theengine in the rear of the mower and caster wheels in the front. Anexample of a zero-radius turn mower is disclosed in Schaedler, et al.,U.S. Pat. No. 7,992,659, which is incorporated herein by specificreference for all purposes.

A standard riding mower with the engine in the front that uses asteering wheel to turn the front wheel has a limited turning radius.Further, the tightest turning radius is only achievable at a moderatespeeds and on ideal surfaces. Under most conditions, the mower tries topush forward and slide the front tires rather than turn in accordancewith the actual turning direction of the front tires. Attempts have beenmade to use a zero turn type transmission with caster wheels on astandard mower; however, on side hills or slopes the front end of themower tends to drift downhill due to the weight of the engine in thefront of the mower, thereby making it difficult to drive in a straightline forward.

To achieve the best cutting performance, most manufacturers recommendcutting grass with the engine at its maximum RPM. This requires atransmission that can vary the ground speed of the mower while theengine RPM is constant. Most prefer a ground speed range of 1 to 6 milesper hour and the mower must be capable of a reverse motion and speedcontrol as well.

The typical riding mower has a steering wheel that is mechanicallyconnected to steering rods or linkages that turn the front wheels andhas a foot pedal that controls the ground speed and direction via ahydrostatic type transmission. However, some mowers use a gearedtransmission that requires the user to shift gears for speed anddirection.

SUMMARY OF INVENTION

In various exemplary embodiments, the present invention comprises acontinuously variable transmission (CVT) system, which turns the rearwheels of a lawn mower or similar vehicle at different speeds in acoordinated method with the front steering wheels in order to achievethe best turning radius (including a tight or zero turn radius, ifdesired) under most conditions. The system of the present invention ismore cost effective and efficient than the zero turn methods and systemsknown in the prior art.

There are several varieties of CVT type systems, such as pulley based,toroidal, friction drive, and hydrostatic systems. These are used inmany types of applications, including but not limited to automobiles,motorcycles, lawnmowers, go karts, as well as industrial uses formachinery and equipment.

In one embodiment, a riding lawnmower uses a pulley-based CVT system.The system includes two stages: the first stage controlling the primaryground speed, and the second stage having dual CVTs (e.g., left andright) that input into dual gear reducers (left and right). The rearwheels are mechanically connected to the output of the reducers (leftand right). The reducers also include a shifting mechanism for forwardand reverse. The second stage dual CVTs (left and right) aresynchronized with the steering wheel, thus achieving different rearwheel speeds and/or directions based on the steering wheel position.

There are two types of pulley-based systems: Fixed Center Distance(FCD), and Adjustable Center Distance (ACD). In a FCD system, twopulleys are in a fixed position relative to each other. The first pulleyis manually adjusted so that the two sheave halves move in and outchanging the pitch diameter of the belt around the first pulley. Thesecond pulley is spring loaded allowing the two sheave halves to move inand out and when the diameter of the first pulley changes the springpressure of the second pulley, it forces the pitch diameter of thesecond pulley to change in accordance with the first. The FCD methodchanges the pitch diameter of the first and second pulley and achievesthe maximum speed ratio. The RPM of the first pulley does not change,but the pitch diameter of the first pulley affects the feet per minutethat the belt travels per revolution. The RPM and pitch diameter of thesecond pulley both change as a result of the feet per minute of the beltand the pitch diameter of the first pulley. The change in feet perminute and/or the RPM change are equivalent to a speed change.

In an ACD system, the center distance between the two pulleys changes.One pulley is similar to an idler pulley in that the pitch diameter doesnot change. The idler pulley moves toward or away from the secondpulley. The second pulley is spring loaded allowing the two sheavehalves to move in and out which changes the pitch diameter. When theidler pulley moves away from the second pulley the belt is pulled towardthe center of the second pulley which makes the pitch diameter smallerthus reducing the feet per minute. Conversely, when the idler pulleymoves toward the second pulley, the spring pressure of the second pulleymoves the belt to the outside of the pulley making the pitch larger andincreasing the feet per minute. In this type of system, the pitchdiameter of only one pulley changes, therefore, typically it onlyachieves half of the ratio change possible with a FCD system.

In one embodiment, the system comprises a CVT transmission that uses aFCD pulley system for both the first and second stages. The first stagepulleys are “A” and “B/C” (a double pulley with “B” being a variablespeed pulley and “C” being a fixed pulley). Pulley “D” is anintermediate pulley. The second stage pulleys are “E”, “F”, “G” and “H”.A belt goes from pulley “A” (which is mounted on the engine shaft) topulley “B” of “B/C” (“B” being the variable speed pulley). Either pulley“A” or “B” in the first stage is mechanically connected to the footpedal on the vehicle, which adjusts the pitch diameters of the firststage pulleys and thus the primary ground speed. Pulley “C” is connectedby a second belt to pulley “D”. Pulley “D” is on a shaft that drivespulleys “E” and “F”. Pulley “E” is connected by a belt to pulley “G”,and pulley “F” is connected to pulley “H”. Pulley “E” or “G” isconnected by a linkage to the left side of the steering plate, and “F”or “H” is connected by a linkage to the right side of the steeringplate. When the steering plate rotates with the steering wheel, thelinkages pull or push in opposite directions a lever on each pulleywhich manually adjusts the pitch diameters of the pulleys. This causesone wheel to speed up and one wheel to slow down in a coordinated methodwith the front steered wheels.

In another embodiment, the system comprises a CVT transmission thatutilizes a FCD pulley system in the first stage and an ACD pulley systemin the second stage. The first stage pulleys are labeled “A” and “B”.The second stage pulleys are labeled “C/E”, “D/F”, “G” and “H”. A beltgoes from pulley “A” (which is connected to the vehicle engine) aroundthe “C” and “D” pulleys, and then to pulley “B”. The speed of “C” and“D” pulleys of the second stage is based on the pitch diameters of thefirst stage pulleys “A” and “B”. One of the pulleys “A’ or “B” in thefirst stage is mechanically connected to the foot pedal which adjuststhe pitch diameters and thus the primary speed. Pulleys “C/E” and “D/F”are double idler pulleys which rotate together and are mounted on asteering plate that rotates with the steering wheel rotation. A beltgoes from “E” to “G” and another belt goes from “F” to “H”. When thesteering plate rotates with the steering wheel it causes the “C/E” and“D/F” pulleys to move toward and away from pulleys “G” and “H” inopposite directions thus changing the pitch diameter of pulleys “G” and“H”. This causes one wheel to speed up and one wheel to slow down in acoordinated method with the front steered wheels.

In yet another embodiment, the system comprises a CVT transmission thatutilizes a FCD pulley system in the first stage and an ACD pulley systemwith gears in the second stage. The first stage pulleys are labeled “A”and “B”. The second stage pulleys are labeled “C”, “D”, “E” and “F”. Abelt goes from pulley “A” (pulley connected to engine) to pulley “B”.One of the pulleys “A” or “B” in the first stage is mechanicallyconnected to the foot pedal which adjusts the pitch diameters and thusthe primary speed. Pulley “B” is mechanically connected by gears topulleys “C” and “D” of the second stage and the speed is based on thepitch diameters of the first stage pulleys “A” and “B”. Pulleys “C” and“D” are idler pulleys which are mounted on a steering plate that rotateswith the steering wheel rotation. A belt goes from “C” to “F” andanother belt goes from “D” to “E”. When the steering plate rotates withthe steering wheel it causes the “C” and “D” pulleys to move toward andaway from pulleys “E” and “F” in opposite directions thus changing thepitch diameter of pulleys “E” and “F”. This causes one wheel to speed upand one wheel to slow down in a coordinated method with the frontsteered wheels.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of a drive system with a FCD pulleysystem for both the first and second stages in accordance with anembodiment of the present invention.

FIG. 2 shows a top view of the drive system of FIG. 1.

FIG. 3 shows a perspective view of a drive system with a FCD pulleysystem for the first stage and an ACD pulley system for the secondstage, in accordance with another embodiment of the present invention.

FIG. 4 shows a top view of the drive system of FIG. 3.

FIG. 5 shows a perspective view of a drive system with a FCD pulleysystem for the first stage and an ACD pulley system with gears for thesecond stage, in accordance with another embodiment of the presentinvention.

FIG. 6 shows a top view of the drive system of FIG. 5.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

In various exemplary embodiments, the present invention comprises acontinuously variable transmission (CVT) system, which turns the rearwheels of a lawn mower or similar vehicle at different speeds in acoordinated method with the front steering wheels in order to achievethe best turning radius (including a tight or zero turn radius, ifdesired) under most conditions. The system of the present invention ismore cost effective and efficient than the zero turn methods and systemsknown in the prior art.

There are several varieties of CVT type systems, such as pulley based,toroidal, friction drive, and hydrostatic systems. These are used inmany types of applications, including but not limited to automobiles,motorcycles, lawnmowers, go karts, as well as industrial uses formachinery and equipment.

In one embodiment, a riding lawnmower uses a pulley-based CVT system.The system includes two stages: the first stage 10 controlling theprimary ground speed, and the second stage 20 having dual CVTs (e.g.,left and right) that input into dual gear reducers 80 (left and right).The rear wheels are mechanically connected to the output of the reducers(left and right). The reducers also include a shifting mechanism forforward and reverse. The second stage dual CVTs (left and right) aresynchronized with the steering wheel, thus achieving different rearwheel speeds and/or directions based on the steering wheel position.

There are two types of pulley-based systems: Fixed Center Distance(FCD), and Adjustable Center Distance (ACD). In a FCD system, twopulleys are in a fixed position relative to each other. The first pulleyis manually adjusted so that the two sheave halves move in and outchanging the pitch diameter of the belt around the first pulley. Thesecond pulley is spring loaded allowing the two sheave halves to move inand out and when the diameter of the first pulley changes the springpressure of the second pulley, it forces the pitch diameter of thesecond pulley to change in accordance the first. The FCD method changesthe pitch diameter of the first and second pulley and achieves themaximum speed ratio. Note that the RPM of the first pulley does notchange, but the pitch diameter of the first pulley affects the feet perminute that the belt travels per revolution. The RPM and pitch diameterof the second pulley both change as a result of the feet per minute ofthe belt and the pitch diameter of the first pulley. The change in feetper minute and/or the RPM change are equivalent to a speed change.

In an ACD system, the center distance between the two pulleys changes.One pulley is similar to an idler pulley in that the pitch diameter doesnot change. The idler pulley moves toward or away from the secondpulley. The second pulley is spring loaded allowing the two sheavehalves to move in and out which changes the pitch diameter. When theidler pulley moves away from the second pulley the belt is pulled towardthe center of the second pulley which makes the pitch diameter smallerthus reducing the feet per minute. Conversely, when the idler pulleymoves toward the second pulley, the spring pressure of the second pulleymoves the belt to the outside of the pulley making the pitch larger andincreasing the feet per minute. In this type of system, the pitchdiameter of only one pulley changes, therefore, typically it onlyachieves half of the ratio change possible with a FCD system.

FIGS. 1 and 2 show a CVT transmission that uses a FCD pulley system forboth the first 10 and second 20 stages. The first stage pulleys 10 are“A” and “B/C”. Pulley “D” is an intermediate pulley. The second stagepulleys 20 are “E”, “F”, “G” and “H”. A belt 30 goes from pulley “A”(which is mounted on the engine shaft 40) to pulley “B” of “B/C” (adouble pulley with “B” being a variable speed pulley and “C” being afixed pulley). Either pulley “A” or “B” in the first stage ismechanically connected 42 to the foot pedal on the vehicle, whichadjusts the pitch diameters of the first stage pulleys and thus theprimary ground speed. Pulley “C” is connected by a second belt 32 topulley “D”. Pulley “D” is on a shaft that drives pulleys “E” and “F”.Pulley “E” is connected by a belt 34 to pulley “G”, and pulley “F” isconnected by a belt 36 to pulley “H”. Pulley “E” or “G” is connected bya linkage 52 to the left side of the steering plate 50, and “F” or “H”is connected by a linkage 54 to the right side of the steering plate 50.When the steering plate rotates with the steering wheel (by means of thesteering shaft 56), the linkages pull or push in opposite directions alever 60 on each pulley which manually adjusts the pitch diameters ofthe pulleys. This causes one wheel to speed up and one wheel to slowdown in a coordinated method with the front steered wheels.

FIGS. 3 and 4 show a CVT transmission that utilizes a FCD pulley systemin the first stage 110 and an ACD pulley system in the second stage 120.The first stage pulleys 110 are labeled “A” and “B”. The second stagepulleys 120 are labeled “C/E”, “D/F”, “G” and “H”. A belt 130 goes frompulley “A” (which is connected to the vehicle engine through the engineshaft 140) around the “C” and “D” pulleys, and then to pulley “B”. Thespeed of “C” and “D” pulleys of the second stage is based on the pitchdiameters of the first stage pulleys “A” and “B”. One of the pulleys “A”or “B” in the first stage is mechanically connected 142 to the footpedal which adjusts the pitch diameters and thus the primary speed.Pulleys “C/E” and “D/F” are double idler pulleys which rotate togetherand are mounted on a steering plate 150 that rotates with the steeringwheel rotation (by means of the steering shaft 156). A belt 134 goesfrom “E” to “G” and another belt 132 goes from “F” to “H”. When thesteering plate 150 rotates (around a pivot 152) with the steering wheel(via the steering shaft 156) it causes the “C/E” and “D/F” pulleys tomove toward and away from pulleys “G” and “H” in opposite directionsthus changing the pitch diameter of pulleys “G” and “H”. This causes onewheel to speed up and one wheel to slow down in a coordinated methodwith the front steered wheels.

FIGS. 5 and 6 show another embodiment of a CVT transmission thatutilizes a FCD pulley system in the first stage 210 and an ACD pulleysystem with gears in the second stage 220. The first stage pulleys arelabeled “A” and “B”. The second stage pulleys are labeled “C”, “D”, “E”and “F”. A belt 230 goes from pulley “A” (pulley is connected to engine)to pulley “B”. One of the pulleys “A” or “B” in the first stage ismechanically connected 242 to the foot pedal which adjusts the pitchdiameters and thus the primary speed. Pulley “B” is mechanicallyconnected by gears 270 to pulleys “C” and “D” of the second stage andthe speed is based on the pitch diameters of the first stage pulleys “A”and “B”. Pulleys “C” and “D” are idler pulleys which are mounted on asteering plate 250 that rotates with the steering wheel rotation. A belt234 goes from “C” to “F” and another belt 232 goes from “D” to “E”. Whenthe steering plate 250 rotates with the steering wheel it causes the “C”and “D” pulleys to move toward and away from pulleys “E” and “F” inopposite directions thus changing the pitch diameter of pulleys “E” and“F”. This causes one wheel to speed up and one wheel to slow down in acoordinated method with the front steered wheels.

Thus, it should be understood that the embodiments and examplesdescribed herein have been chosen and described in order to bestillustrate the principles of the invention and its practicalapplications to thereby enable one of ordinary skill in the art to bestutilize the invention in various embodiments and with variousmodifications as are suited for particular uses contemplated. Eventhough specific embodiments of this invention have been described, theyare not to be taken as exhaustive. There are several variations thatwill be apparent to those skilled in the art.

What is claimed is:
 1. A continuously variable transmission (CVT) systemfor a small vehicle with an engine and engine shaft, a steering wheelmechanically connected to a steering plate, and a right and left rearwheel, comprising: a primary stage comprising a fixed center distance(FCD) pulley system with at least two pulleys, a first primary stagepulley and a second primary stage pulley, wherein the first primarystage pulley is mechanically connected to the engine or engine shaft,and the first and second stage pulleys are connected by a first belt;and a secondary stage mechanically connected to said primary stage, saidsecondary stage comprising an adjustable center distance (ACD) pulleysystem with at least two gears, and with at least four pulleys arrangedin right and left pairs, each pair comprising a front and back pulleyconnected by a right or left second belt, wherein the front pulley ofeach pair is connected to a corresponding gear, and further wherein theback pulley of each pair is mechanically connected to the right or leftrear wheels of the vehicle, respectively; wherein the pitch diameters ofsome or all of the pulleys in the secondary stage are changed inresponse to rotation of the steering plate, causing one of the rearwheels to speed up and the other rear wheel to slow down in acoordinated manner.
 2. The system of claim 1, wherein either said firstor second primary stage pulley is mechanically connected to a speedcontrol pedal on the vehicle.
 3. The system of claim 1, wherein the backpulley of each pair of pulleys in the secondary stage is mechanicallyconnected to a reducer, which is mechanically connected to therespective rear wheel.
 4. The system of claim 1, wherein the frontpulleys of the secondary stage are dual idler pulleys mounted on thesteering plate, each with a first idler pulley part and a second idlerpulley part, and the first belt extends from the first primary stagepulley to the first part of the right front secondary stage idler pulleyto the second primary stage pulley to the first part of the left frontsecondary stage idler pulley.
 5. The system of claim 4, wherein thesecond idler pulley part of each of the front pulleys of the secondarystage is connected by the right or left second belt to the respectiveback pulleys.
 6. The system of claim 5, wherein rotation of the steeringplate causes the right and left dual idler pulleys to move toward andaway from their respective back pulleys in opposite directions, therebychanging the pitch diameter of the pulley.
 7. The system of claim 1,wherein the front pulleys of the secondary stage are idler pulleysmounted on the steering plate, and are further connected by individualgears to the second primary stage pulley.
 8. The system of claim 7,wherein rotation of the steering plate causes the respective right andleft idler pulleys to move toward and away from their respective backpulleys in opposite directions, thereby changing the pitch diameter ofthe pulley.
 9. The system of claim 1, further wherein the second primarystage pulley is mechanically connected to said at least two gears in thesecondary stage.
 10. The system of claim 1, further comprising a thirdgear mechanically connecting the second primary stage pulley to said atleast two gears in the secondary stage.